A structure commonly formed during the manufacture of semiconductor devices such as microprocessors, memory devices, and logic devices includes a plug or stud manufactured from polycrystalline silicon (poly) or metal such as tungsten. For purposes of illustration only, this disclosure discusses the formation of a plug from poly. The plug typically contacts a doped layer in a semiconductor substrate or contacts some other underlying structure. To manufacture the plug, a masked dielectric layer is formed over the underlying structure and an etch is completed to form a hole in the dielectric which exposes the underlying structure to which contact is to be made. A blanket poly layer is deposited over the dielectric layer which fills the hole in the dielectric layer and contacts the underlying structure. The poly is then removed from a planar surface of the dielectric, typically using a chemical mechanical polishing (CMP) process which leaves the plug formed within the dielectric layer.
Ideally, the process described above would leave a poly plug having a upper surface which is flush with the upper level of the dielectric layer. CMP results in a sufficiently-flush plug but it is not a particularly clean or uniform process and, in practice, can damage surface structures. Previous dry etches are cleaner than CMP but can result in a plug having a concave upper surface which is recessed into the dielectric layer. It is difficult to form a reliable electrical connection to a recessed plug with a subsequently formed layer such as metal.
Another problem with the process described above results from surface defects in the dielectric, such as surface scratches, cracks, or other voids or recesses formed during manufacture of the dielectric layer. During conductor formation these surface defects are filled with poly which remains in the void after CMP removal of the poly from the surface of the dielectric. The poly remaining in the voids, also referred to as "stringers," can form a short between other conductive structures such as between two or more plugs or between other structures such as metal lines which are subsequently formed.
A method for forming a conductive plug or stud which reduces or eliminates the problems described above would be desirable.